It is known that diamond material possesses desirable mechanical, electrical and thermal properties for application to integrated circuitry. WO 94/15359 published 7 Jul. 1994, "Silicon On Diamond Circuit Structure", assigned to the assignee of the present application, which discloses a method for forming an integrated circuit structure having a layer of crystalline silicon formed over a diamond layer. Among other applications, such a structure is useful for providing heat dissipation paths of enhanced thermal conductivity. Resulting advantages include increased power handling capability and higher levels of device integration.
More generally, integrated circuits fabricated on semiconductor-on-insulator (SOI) structures offer performance advantages including freedom from latchup for CMOS circuits, low parasitic capacitance, low power consumption, radiation hardness, high temperature operation, high voltage operation and the possibility of multi-layer device integration. Commonly, in SOI structures, device islands are formed by extending isolation trenches through the device semiconductor layer down to an insulation level. Sidewalls for such trenches are formed with an insulator such as silicon dioxide.
Fabrication of silicon-on-diamond structures may begin with preparation of a wafer growth substrate for receiving a polycrystalline diamond film thereover. After deposition of the diamond material, e.g., by Plasma Enhanced Chemical Vapor Deposition (PECVD), a thin polycrystalline or amorphous silicon film is formed over the diamond layer, perhaps to a thickness of less than one micron. Next, the silicon film is prepared to provide a smooth bonding surface for receiving a second wafer. The second wafer includes a semiconductor layer of suitable quality for formation of integrated circuit devices thereon. Further details are disclosed in WO 94/15359 now incorporated herein by reference. Generally, the wafer substrate upon which the diamond film is grown becomes an integral part of the SOI structure.
Other techniques for fabricating silicon on insulator devices using bonded wafers with a diamond layer and a silicon dioxide or silicon nitride layer on the diamond layer are shown in Research Disclosure No. 345, January 1993, page 76, Abstract No. 345114 and WO 91/11822. Techniques for oxide bonding and silicide bonding are described, respectively, in Japanese Journal of Applied Physics Vol. 30, No. 10A, Part 2, 10 Oct. 1991, pages L1693-L1695 and IEDM 1986, pages 210-213. Another technique shown in EP-A-0317124 forms a silicon on diamond device using traditional deposition and removal steps without bonding two wafers together.
For the above-referenced process, deposition conditions must be carefully chosen to assure adhesion of the diamond film to the wafer substrate and to minimize warpage of the substrate once the diamond deposition is complete. Subsequent processing to form integrated circuit devices on the SOI structure has limited the choice of growth substrate materials to those compatible with the processing environment.
It is now recognized that the optimal film characteristics desired for application of diamond as a buried insulator in an SOI structure are not necessarily consistent with the characteristics imposed by the growth substrate bonded thereto. For example, due to differences in materials properties, e.g., thermal expansion characteristics, thermal cycling may limit the variety of wafer substrate types which are compatible with the formation of diamond layers.
To acquire improved characteristics there is now provided a method for preparing a semiconductor-on-insulator structure beginning with provision of a removable deposition surface and formation of diamond material thereon. The resulting diamond layer includes first and second opposing surfaces with the first surface initially in contact with the deposition surface. The first surface of the diamond layer is separated from the deposition surface. A bond is formed between one of the diamond surfaces and a wafer structure comprising a layer of semiconductor material.
Structures and methods are also provided for protecting the integrity of diamond material during semiconductor processing and for preventing diffusion of carbon from the diamond material into another layer of a semiconductor structure. Generally, an integrated circuit structure comprises a layer of diamond, a layer of silicon nitride formed on the diamond and a layer of semiconductor material over the nitride layer. According to one embodiment of the invention, the structure may be fabricated by first depositing a layer of diamond material and forming silicon nitride over the layer. A layer or wafer of semiconductor material is bonded to the diamond layer with the nitride layer positioned at the interface. Alternately, after depositing the diamond-containing layer and bonding a semiconductor layer to the diamond layer, trenches are formed through the semiconductor material to the diamond layer and silicon nitride is deposited in the trenches.